Surface-mount type antenna and antenna apparatus

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a compact surface-mount type antenna and an antenna apparatus for use in mobile communication equipment such as a cellular phone.

2. Description of the Related Art

In keeping with rapid advancement of down-sized mobile communication equipment such as a cellular phone, miniaturization has been underway in an antenna which constitutes such equipment. Thus, for example, a surface-mount type antenna has hitherto been developed. Now, a conventional surface-mount type antenna and an antenna apparatus incorporating it will be described with reference to a perspective view shown in FIG.

8

.

In

FIG. 8

, reference numeral

50

denotes a surface-mount type antenna. This surface-mount type antenna

50

is mounted on a mounting substrate

56

, thus constituting an antenna apparatus

61

. In the surface-mount type antenna

50

shown in

FIG. 8

, reference numeral

51

denotes a substantially prismatic base body; reference numeral

52

denotes a feeding terminal; reference numeral

53

denotes a ground terminal; and reference numeral

54

denotes a radiating electrode. Moreover, in the mounting substrate

56

, reference numeral

57

denotes a substrate; reference numeral

58

denotes a feeding electrode; reference numeral

59

denotes a ground electrode; and reference numeral

60

denotes a ground conductor layer.

In the conventional surface-mount type antenna

50

, the feeding terminal

52

and the ground terminal

53

are formed on a side surface of the base body

51

. The radiating electrode

54

, which is routed as a slim conductor pattern, is configured as follows. At first it extends upwardly from the ground terminal

53

on the side surface, and is then substantially U-shaped, as viewed plane-wise, on a top surface of the base body

51

so as to take substantially the form of a loop, and eventually returns to the side surface once again to extend downwardly toward the feeding terminal

52

. Moreover, the radiating electrode

54

has a gap

55

formed in a certain position thereof close to the feeding terminal

52

. Thereby, the capacitance of the radiating electrode

54

can be so adjusted that impedance matching is achieved between the radiating electrode

54

and the feeding electrode

58

(feeding line) of the mounting substrate

56

.

On the other hand, in the mounting substrate

56

, on a surface of the substrate

57

are formed the feeding electrode

58

, the ground electrode

59

, and the ground conductor layer

60

. The ground conductor layer

60

is arranged on one side of the ground electrode

59

so as to be connected thereto.

Then, the surface-mount type antenna

50

is mounted, with the feeding terminal

52

connected to the feeding electrode

58

and the ground terminal

53

connected to the ground electrode

59

, on the surface of the mounting substrate

56

, thus constituting the antenna apparatus

61

.

In the conventional surface-mount type antenna

50

, however, since the radiating electrode

54

is made short, there is a tendency of an operating frequency to increase. To decrease the operating frequency, the base body

51

needs to have a higher dielectric constant, or the radiating electrode

54

needs to be slimmed down.

However, an increase in the dielectric constant of the base body

51

gives rise to a problem of the antenna characteristics being abruptly changed to narrow-band characteristics. On the other hand, slimming of the radiating electrode

54

gives rise to a problem of great radiation loss.

Moreover, by adjusting a size of the gap

55

which is formed in the radiating electrode

54

to achieve impedance matching between the radiating electrode

54

and the feeding electrode

58

, the impedance of the radiating electrode

54

can be changed. In this case, however, a resonant frequency of the antenna varies with the change of the impedance. This makes it difficult to attain the desired antenna characteristics as designed.

SUMMARY OF THE INVENTION

The invention has been devised in view of the above-described problems with the conventional art, and accordingly its object is to provide a surface-mount type antenna and an antenna apparatus capable of attaining satisfactory antenna characteristics with stability, of enhancing radiation efficiency, and of achieving miniaturization.

The invention provides a surface-mount type antenna comprising:

a base body made of a dielectric or magnetic material having a substantially rectangular solid shape;

a feeding terminal formed at one end of one side surface of the base body;

a ground terminal formed at another end of the one side surface of the base body;

a radiating electrode which has its one end connected to the ground terminal, the radiating electrode being disposed helically across the surfaces of the base body in such a way that it extends from the one side surface, across one principal surface, another side surface which is opposite to the one side surface, and another principal surface which is opposite to the one principal surface, and then returns to the one side surface and further extends, through the one principal surface, toward the one end of the one side surface; and

a wide-area portion,

wherein another end of the radiating electrode extends from the one principal surface, through the other side surface, toward the other principal surface, so as to form the wide-area portion facing the feeding terminal.

According to the invention, the radiating electrode is disposed helically across the surfaces of the base body in such a way that it extends from the one side surface, across the one principal surface, the other side surface, and the other principal surface, and then returns to the one side surface and further extends, through the one principal surface, toward the one end of the one side surface, and further the other feeding-terminal-side end of the radiating electrode extends across the surfaces of the base body, i.e., extends from the one principal surface, through the other side surface, toward the other principal surface, so as to form the wide-area portion facing the feeding terminal. With this configuration, the radiating electrode can be made longer, and also the wide-area portion of the radiating electrode can be electro magnetically coupled to the feeding terminal through an electric capacitance generated therebetween. Moreover, at the time of mounting on the mounting substrate, since a large capacitance can be created between the wide-area portion of the radiating electrode and the ground conductor layer of the mounting substrate, the resonant frequency of the radiating electrode can be decreased. This makes it possible to achieve miniaturization of the antenna without increasing the dielectric constant of the base body and without excessively slenderizing the radiating electrode.

Further, according to the invention, the impedance matching between the radiating electrode and the feeding electrode (feeding line) of the mounting substrate on which the radiating electrode is mounted can be achieved by adjusting the capacitance between the radiating electrode and the feeding terminal. The capacitance adjustment can be made by adjusting the configuration and/or area of the wide-area portion of the radiating electrode. Meanwhile, a dominant factor in the magnitude of the resonant frequency of the antenna is the capacitance between the radiating electrode and the ground conductor layer of the mounting substrate. Hence, variation in the resonant frequency resulting from the impedance adjustment by means of the wide-area portion can be minimized. As a result, it is possible to obtain a compact surface-mount type antenna that provides higher radiation efficiency and stable antenna characteristics.

In the invention, it is preferable that a width of the wide-area portion is adjusted to be three to ten times that of a conductor portion of the radiating electrode having a helical conformation.

According to the invention, the capacitance between the wide-area portion and the feeding terminal or the ground conductor layer can be increased, thus achieving satisfactory electromagnetic coupling with the feeding terminal.

In the invention, it is preferable that a length of the wide-area portion which lies on the other principal surface of the base body, extending from the other side surface-side to the one side surface-side, is determined such that the distance to the one side surface is equal to or greater than 1 mm.

According to the invention, it is possible to prevent occurrence of frequency variation which is caused by capacitance variation between the wide-area portion and the ground conductor layer resulting from antenna-mounting positional variation.

In the invention, it is preferable that the base body is made of a dielectric material having a relative dielectric constant εr which is kept within a range from 3 to 30.

According to the invention, an effective length of the radiating electrode is decreased, and thus the current distribution region is increased in area. This allows the radiating electrode to emit a larger quantity of radio waves, resulting in advantages in enhancing a gain of the antenna and in achieving miniaturization of the surface-mount type antenna.

In the invention, it is preferable that the base body is made of a magnetic material having a relative magnetic permeability μr which is kept within a range from 1 to 8.

According to the invention, the radiating electrode has a higher impedance, which results in a low Q factor in the antenna, and the bandwidth is accordingly increased.

The invention further provides an antenna apparatus comprising:

a mounting substrate formed thereon a feeding electrode, a ground electrode, and a ground conductor layer which is connected to the ground electrode and arranged on one side of the mounting substrate with respect to the ground electrode; and

the surface-mount type antenna of the invention as mentioned above,

wherein the antenna apparatus is constructed by mounting the surface-mount type antenna on the mounting substrate, with its other principal surface arranged on another side of the mounting substrate with respect to the ground electrode, and simultaneously connecting the feeding terminal and the ground terminal to the feeding electrode and the ground electrode, respectively.

The invention still further provides an antenna apparatus comprising:

a mounting substrate formed thereon a feeding electrode, a ground electrode, and a ground conductor layer which is connected to the ground electrode and arranged on one side of the mounting substrate with respect to the ground electrode; and

the surface-mount type antenna of the invention as mentioned above,

wherein the antenna apparatus is constructed by mounting the surface-mount type antenna on the mounting substrate, with its one principal surface arranged on another side of the mounting substrate with respect to the ground electrode, and simultaneously connecting the feeding terminal and the ground terminal to the feeding electrode and the ground electrode, respectively.

According to the invention, the antenna apparatus is constructed as follows. The surface-mount type antenna of the invention is mounted on the mounting substrate formed thereon the feeding electrode, the ground electrode, and the ground conductor layer which is connected to the ground electrode and arranged on the one side of the mounting substrate with respect to the ground electrode. Simultaneously, the feeding terminal and the ground terminal are connected to the feeding electrode and the ground electrode, respectively. With this structure, by adjusting the capacitance created between the radiating electrode of the surface-mount type antenna having the wide-area portion and the feeding electrode, ground electrode, and ground conductor layer of the mounting substrate, impedance matching can be achieved between the radiating electrode and the feeding electrode. Moreover, proper setting and adjustment of the resonant frequency and radiation efficiency of the radiating electrode, as well as miniaturization, can be achieved with ease. As a result, it is possible to obtain a compact antenna apparatus that provides higher radiation efficiency and stable antenna characteristics.

In the invention, it is preferable that the surface-mount type antenna is mounted on the mounting substrate at a distance of 0.5 mm to 3 mm from an end of the ground conductor layer of the mounting substrate.

According to the invention, the antenna apparatus is operable at a frequency band of 1 GHz to 10 GHz.

In the invention, it is preferable that the surface-mount type antenna is so mounted as to protrude from an edge of the ground conductor layer.

According to the invention, the bandwidth and gain of the antenna can be enhanced.

As described heretofore, according to the invention, it is possible to provide a surface-mount type antenna and an antenna apparatus capable of attaining satisfactory antenna characteristics with stability, of enhancing radiation efficiency, and of achieving miniaturization.

BRIEF DESCRIPTION OF THE DRAWINGS

Other and further objects, features, and advantages of the invention will be more explicit from the following detailed description taken with reference to the drawings wherein:

FIG. 1

is a perspective view showing a surface-mount type antenna of a first embodiment according to the invention, and also an antenna apparatus of a first embodiment according to the invention which is constituted by mounting the surface-mount type antenna on a surface of a mounting substrate;

FIGS. 2A through 2D

are plan views showing each of the principal and side surfaces of the surface-mount type antenna of the first embodiment according to the invention;

FIG. 3

is a plan view showing the mounting substrate;

FIG. 4

is a perspective view showing an surface-mount type antenna of a second embodiment according to the invention, and also an antenna apparatus of a second embodiment according to the invention which is constituted by mounting the surface-mount type antenna on the surface of the mounting substrate;

FIGS. 5A through 5D

are plan views showing each of the principal and side surfaces of the surface-mount type antenna of the second embodiment according to the invention;

FIG. 6

is a plan view showing the mounting substrate;

FIG. 7

is a schematic equivalent circuit diagram for explaining a function of the antenna structure in the surface-mount type antenna and the antenna apparatus according to the invention; and

FIG. 8

is a perspective view showing one example of a conventional surface-mount type antenna and an antenna apparatus incorporating the conventional antenna.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now referring to the drawings, preferred embodiments of the invention are described below.

FIG. 1

is a perspective view showing a surface-mount type antenna of a first embodiment according to the invention, and also an antenna apparatus of a first embodiment according to the invention which is constituted by mounting the surface-mount type antenna on a surface of a mounting substrate.

FIGS. 2A through 2D

are plan views showing each of the principal and side surfaces of the surface-mount type antenna of the first embodiment according to the invention.

FIG. 3

is a plan view showing the mounting substrate.

In

FIGS. 1 and 2A

through

2

D, reference numeral

10

denotes a surface-mount type antenna according to the invention; reference numeral

11

denotes a base body made of a dielectric or magnetic material having a substantially rectangular solid shape; reference numeral

12

denotes a feeding terminal formed at one end

11

e

of one side surface (corresponding to a left-hand front surface, in

FIG. 1

)

11

a

of the base body

11

; reference numeral

13

denotes a ground terminal formed at another end

11

f

of the one side surface

11

a

; and reference numeral

14

denotes a radiating electrode which is formed of a line-shaped conductor. The radiating electrode

14

has its one end connected to the ground terminal

13

, and is disposed helically across the surfaces of the base body

11

. More specifically, the radiating electrode

14

extends from the one. side surface

11

a

, across one principal surface (corresponding to a top surface, in

FIG. 1

)

11

b

adjacent to the one side surface

11

a

; another side surface

11

c

which is opposite to the one side surface

11

a

; and another principal surface (corresponding to a bottom surface, in

FIG. 1

)

11

d

which is opposite to the one principal surface

11

b

, and then returns to the one side surface

11

a

and further extends, through the one principal surface

11

b

, toward the one end lie of the one side surface

11

a

(the feeding-terminal

12

side) In addition, reference numeral

15

denotes a wide-area portion formed at the other end of the radiating electrode

14

.

Moreover, in

FIGS. 1 and 3

, reference numeral

16

denotes a mounting substrate; reference numeral

17

denotes a substrate; reference numeral

18

denotes a feeding electrode formed on the surface of the substrate

17

; reference numeral

19

denotes aground electrode; and reference numeral

20

denotes a ground conductor layer which is connected to the ground electrode

19

and arranged on one side (corresponding to the left-hand front side, in

FIG. 1

)

17

a

of the substrate

17

with respect to the ground electrode

19

.

That is, the surface-mount type antenna

10

according to the invention includes: the base body

11

; the feeding terminal

12

; the ground terminal

13

; the radiating electrode

14

; and the wide-area portion

15

. The base body

11

is made of a dielectric or magnetic material having a substantially rectangular solid shape. The feeding terminal

12

is formed at the one end

11

e

of the one side surface

11

a

of the base body

11

. The ground terminal

13

is formed at the other end

11

f

of the one side surface

11

a

of the base body

11

. The radiating electrode

14

, which is formed of a line-shaped conductor and has its one end connected to the ground terminal

13

, is disposed helically across the surfaces of the base body

11

as follows. The radiating electrode

14

extends from the one side surface la, across the one principal surface

11

b

; the other side surface

11

c

; and the other principal surface

11

d

, and then returns to the one side surface

11

a

and further extends, through the one principal surface

11

b

, toward the one end

11

e

of the one side surface

11

a

. The wide-area portion

15

is formed at the other end of the radiating electrode

14

.

Moreover, the mounting substrate

16

includes: the substrate

17

; the feeding electrode

18

; the ground electrode

19

; and the ground conductor layer

20

. The feeding electrode

18

is formed on the surface of the substrate

17

. The ground electrode

19

is formed on the surface of the substrate

17

. The ground conductor layer

20

is formed on the surface of the substrate

17

. More specifically, the ground conductor layer

20

is connected to the ground electrode

19

and arranged on the one side

17

a

of the substrate

17

with respect to the ground electrode

19

.

Then, the surface-mount type antenna

10

according to the invention is mounted on the surface of the mounting substrate

16

, with its other principal surface

11

d

arranged on another side (corresponding to the right-hand rear side, in

FIG. 1

)

17

b

of the substrate

17

with respect to the ground electrode

19

. Simultaneously, the feeding terminal

12

and the ground terminal

13

are connected to the feeding electrode

18

and the ground electrode

19

, respectively. Thereupon, an antenna apparatus

21

of the first embodiment according to the invention is realized.

A remarkable feature of the surface-mount type antenna

10

according to the invention is that the other end of the radiating electrode

14

extends across the three surfaces of the base body

11

, i.e., extends from the one principal surface

11

b

, through the other side surface

11

c

, toward the other principal surface lid, to form the wide-area portion

15

facing the feeding terminal

12

.

Being disposed face to face with the feeding terminal

12

via the base body

11

, the wide-area portion

15

of the radiating electrode

14

is electro magnetically coupled to the feeding terminal

12

through an electric capacitance generated therebetween. To increase the capacitance between the wide-area portion

15

of the radiating electrode

14

and the feeding terminal

12

or the ground conductor layer

20

, the width of the wide-area portion

15

is adjusted to be three to ten times that of the slim conductor portion of the radiating electrode

14

having a helical conformation. Moreover, the length of the wide-area portion

15

which lies on the one principal surface

11

b

of the base body

11

, extending from the other side surface

11

c

-side to the one side surface

11

a

-side, is determined such that the capacitance between the radiating electrode

14

and the feeding terminal

12

can be so adjusted as to achieve optimal impedance matching. Further, the length of the wide-area portion

15

which lies on the other principal surface lid of the base body

11

, extending from the other side surface

11

c

-side to the one side surface

11

a

-side, is preferably determined such that the distance between the portion and the one side surface

11

a

is equal to or greater than 1 mm. This is because, since variation in capacitance between the wide-area portion

15

of the radiating electrode

14

and the ground conductor layer

20

leads to frequency variation, if the distance to the ground conductor layer

20

is unduly short, antenna-mounting positional variation may result, which causes frequency variation.

Then, the surface-mount type antenna

10

according to the invention thus constructed is mounted on the surface of the mounting substrate

16

at a distance of approximately 0.5 mm to 3 mm, for example, from the end of the ground conductor layer

20

. Simultaneously, the ground terminal

13

is connected via the ground electrode

19

to the ground conductor layer

20

. Thereupon, the antenna apparatus

21

of the first embodiment according to the invention is operable at a frequency band of approximately 1 GHz to 10 GHz, for example.

FIG. 4

is a perspective view, alike to

FIG. 1

, showing an surface-mount type antenna of a second embodiment according to the invention, and also an antenna apparatus of a second embodiment according to the invention which is constituted by mounting the surface-mount type antenna on the surface of the mounting substrate.

FIGS. 5A through 5D

are plan views showing each of the principal and side surfaces of the surface-mount type antenna of the second embodiment according to the invention.

FIG. 6

is a plan view showing the mounting substrate.

In

FIGS. 4 and 5A

through

5

D, reference numeral

30

denotes a surface-mount type antenna according to the invention; reference numeral

31

denotes a base body made of a dielectric or magnetic material having a substantially rectangular solid shape; reference numeral

32

denotes a feeding terminal formed at one end

31

e

of one side surface (corresponding to a left-hand front surface, in

FIG. 4

)

31

a

of the base body

31

; reference numeral

33

denotes a ground terminal formed at another end

31

f

of the one side surface

31

a

; and reference numeral

34

denotes a radiating electrode which is formed of a line-shaped conductor. The radiating electrode

34

has its one end connected to the ground terminal

33

, and is disposed helically across the surfaces of the base body

31

. More specifically, the radiating electrode

34

extends from the one side surface

31

a

, across one principal surface (corresponding to a bottom surface, in

FIG. 4

)

31

b

adjacent to the one side surface

31

a

; another side surface

31

c

which is opposite to the one side surface

31

a

; and another principal surface (corresponding to a top surface, in

FIG. 4

)

31

d

which is opposite to the one principal surface

31

b

, and then returns to the one side surface

31

a

and further extends, through the one principal surface

31

b

, toward the one end

31

e

of the one side surface

31

a

(the feeding-terminal

32

side). In addition, reference numeral

35

denotes a wide-area portion formed at the other end of the radiating electrode

34

.

Moreover, in

FIGS. 4 and 6

, reference numeral

36

denotes a mounting substrate; reference numeral

37

denotes a substrate; reference numeral

38

denotes a feeding electrode formed on the surface of the substrate

37

; reference numeral

39

denotes a ground electrode; and reference numeral

40

denotes a ground conductor layer which is connected to the ground electrode

39

and arranged on one side (corresponding to the left-hand front side, in

FIG. 4

)

37

a

of the substrate

37

with respect to the ground electrode

39

.

That is, the surface-mount type antenna

30

according to the invention includes: the base body

31

; the feeding terminal

32

; the ground terminal

33

; the radiating electrode

34

; and the wide-area portion

35

. The base body

31

is made of a dielectric or magnetic material having a substantially rectangular solid shape. The feeding terminal

32

is formed at the one end

31

e

of the one side surface

31

a

of the base body

31

. The ground terminal

33

is formed at the other end

31

f

of the one side surface

31

a

of the base body

31

. The radiating electrode

34

, which is formed of a line-shaped conductor and has its one end connected to the ground terminal

33

, is disposed helically across the surfaces of the base body

31

as follows. The radiating electrode

34

extends from the one side surface

31

a

, across the one principal surface

31

b

; the other side surface

31

c

; and the other principal surface

31

d

, and then returns to the one side surface

31

a

and further extends, through the one principal surface

31

b

, toward the one end

31

e

of the one side surface

31

a

. The wide-area portion

35

is formed at the other end of the radiating electrode

34

.

Moreover, the mounting substrate

36

includes: the substrate

37

; the feeding electrode

38

; the ground electrode

39

; and the ground conductor layer

40

. The feeding electrode

38

is formed on the surface of the substrate

37

. The ground electrode

39

is formed on the surface of the substrate

37

. The ground conductor layer

40

is formed on the surface of the substrate

37

. More specifically, the ground conductor layer

40

is connected to the ground electrode

39

and arranged on the one side

37

a

of the substrate

37

with respect to the ground electrode

39

.

Then, the surface-mount type antenna

30

according to the invention is mounted on the surface of the mounting substrate

36

, with its one principal surface

31

b

arranged on another side (corresponding to the right-hand rear side, in

FIG. 4

)

37

b

of the substrate

37

with respect to the ground electrode

39

. Simultaneously, the feeding terminal

32

and the ground terminal

33

are connected to the feeding electrode

38

and the ground electrode

39

, respectively. Thereupon, an antenna apparatus

41

of the second embodiment according to the invention is realized.

Also in the antenna apparatus

41

of the invention, a remarkable feature of the surface-mount type antenna

30

of the invention is that the other end of the radiating electrode

34

extends across the three surfaces of the base body

31

, i.e., extends from the one principal surface

31

b

, through the other side surface

31

c

, toward the other principal surface

31

d

, to form the wide-area portion

35

facing the feeding terminal

32

. The wide-area portion

35

is constructed basically in the same manner as the wide-area portion

15

in the surface-mount type antenna

10

of the invention shown in FIG.

1

.

In the antenna apparatus

41

of the invention, the surface-mount type antenna

30

of the invention has basically the same structure as the surface-mount type antenna

10

of the invention shown in

FIG. 1

, the difference being the orientation of the helical conformation of the radiating electrode

34

. Just as is the case with the antenna apparatus

21

of the invention, the surface-mount type antenna

30

of the invention is mounted on the surface of the mounting substrate

36

at a distance of approximately 0.5 mm to 3 mm, for example, from the end of the ground conductor layer

40

. Simultaneously, the ground terminal

33

is connected via the ground electrode

39

to the ground conductor layer

40

. Thereupon, the antenna apparatus

41

is operable at a frequency band of approximately 1 GHz to 10 GHz, for example.

With reference to the schematic equivalent circuit diagram shown in

FIG. 7

, a description will be given below as to a function of the antenna structure in the surface-mount type antenna

10

,

30

and the antenna apparatus

21

,

41

.

In

FIG. 7

, reference symbol L

1

denotes an inductance of the radiating electrode

14

,

34

extending helically across the surfaces of the base body

11

,

31

through the ground conductor layer

20

,

40

, the ground electrode

19

,

39

, and the ground terminal

13

,

33

; reference symbol C

2

denotes a capacitance of the radiating electrode

14

,

34

, which is generated mainly between the wide-area portion

15

,

35

and the ground conductor layer

20

,

40

; and reference symbol C

1

denotes a capacitance of the radiating electrode

14

,

34

, which is generated mainly between the wide-area portion

15

,

35

and the feeding terminal

12

,

32

. Note that between the capacitance C

1

and the ground is connected a high-frequency signal power supply. The equivalent circuit further includes a radiation resistance of the radiating electrode

14

,

34

(not shown).

The radiating electrode

14

,

34

of the surface-mount type antenna

10

,

30

of the invention has the helically extending portion and the wide-area portion

15

,

35

. Therefore, the operating frequency of the antenna can be decreased by obtaining the inductance L

1

and also by creating the capacitance C

2

between the radiating electrode

14

,

34

and the ground conductor layer

20

,

40

. Here, by forming the helically extending portion to realize the inductance L

1

, the self-inductance can be enhanced efficiently, thus achieving miniaturization of the surface-mount type antenna

10

,

30

. Moreover, the radiating electrode

14

,

34

has its other end, where the high-frequency signal current flowing onto the conductor is few in quantity, formed into the wide-area portion

15

,

35

having a larger area. This helps increase the capacitance C

2

generated between the wide-area portion

15

,

35

and the ground conductor layer

20

,

40

. Thereby, a resonant frequency, which is dependent on the inductance L

1

and the capacitance C

2

, is decreased, thus achieving miniaturization of the surface-mount type antenna

10

,

30

and the antenna apparatus

21

,

41

.

In the surface-mount type antenna

10

,

30

and the antenna apparatus

21

,

41

according to the invention, the resonant frequency of the radiating electrode

14

,

34

is defined as an operating frequency of the antenna. Thus, the operating frequency of the antenna is proportional to the reciprocal of the square root of the product of the inductance L

1

and the capacitance C

2

. It will thus be seen that an antenna of satisfactory compactness based on the surface-mount type antenna

10

,

30

and the antenna apparatus

21

,

41

according to the invention can be realized by increasing the inductance L

1

and the capacitance C

2

.

As is well known, slenderizing the conductor pattern of the radiating electrode

14

,

34

is effective in increasing its inductance component L

1

. On the basis of this fact, in the surface-mount type antenna

10

,

30

, the conductor pattern takes on a helical conformation to realize the desired inductance L

1

. This makes it possible to reduce the volume of the base body

11

,

31

, thus achieving miniaturization of the antenna.

On the other hand, the capacitance C

2

is a capacitance component created between the ground conductor layer

20

,

40

of the mounting substrate

16

,

36

and the wide-area portion

15

,

35

of the radiating electrode

14

,

34

. The capacitance value of the capacitance C

2

can be increased by making the wide-area portion

15

,

35

larger in area or by arranging the wide-area portion

15

,

35

in proximity to the ground conductor layer

20

,

40

. However, in the case where the value of the capacitance C

2

is increased by arranging the wide-area portion

15

,

35

in proximity to the ground conductor layer

20

,

40

, variation in the mounting position of the surface-mount type antenna

10

,

30

with respect to the mounting substrate

16

,

36

significantly contributes to variation in the value of the capacitance C

2

. As a result, the center frequency of the antenna is undesirably varied.

Accordingly, as is achieved in the surface-mount type antenna

10

,

30

of the invention and the antenna apparatus

21

,

41

of the invention incorporating the antenna, it is preferable that the distance between the wide-area portion

15

,

35

and the ground conductor layer

20

,

40

is determined such that the influence of variation in the mounting position of the surface-mount type antenna

10

,

30

with respect to the mounting substrate

16

,

36

becomes negligible, and the capacitance C

2

value is increased by making the wide-area portion

15

,

35

larger in area.

Moreover, impedance matching between the feeding line, which is connected to the feeding electrode

18

,

38

to which the feeding terminal

12

,

32

is connected, and the radiating electrode

14

,

34

can be achieved by adjusting the magnitude of the electromagnetic coupling. In the invention, to achieve the impedance matching, the capacitance C

1

is set at an appropriate value by adjusting the configuration, area, and position of the wide-area portion

15

,

35

.

In the surface-mount type antenna

10

,

30

of the invention, the capacitance C

1

existing between the wide-area portion

15

,

35

of the radiating electrode

14

,

34

, and the feeding terminal

12

,

32

is created to adjust the impedance of the radiating electrode

14

,

34

so that the radiating electrode

14

,

34

is excited efficiently. The impedance of the radiating electrode

14

,

34

can be adjusted by changing the capacitance C

1

properly. The capacitance C

1

is changed by varying an interval between the wide-area portion

15

,

35

and the feeding terminal

12

,

32

. Also in this case, since the resonant frequency of the antenna is fixed at a certain value on the basis of the capacitance C

2

, it never occurs that the resonant frequency of the antenna is varied greatly with the change of the impedance of the radiating electrode

14

,

34

. As a result, according to the surface-mount type antenna

10

,

30

and the antenna apparatus

21

,

41

according to the invention, not only it is possible to achieve miniaturization, but it is also possible to attain the desired antenna characteristics as designed.

In the surface-mount type antenna

10

,

30

of the invention, the base body

11

,

31

is made of a dielectric or magnetic material having a substantially rectangular solid shape. For example, there is prepared a dielectric material which is predominantly composed of alumina (relative dielectric constant: 9.6). Such a material in powder form is subjected to pressure-molding and firing treatment to obtain ceramics. Using the ceramics, the base body

11

,

31

is fabricated. In the alternative, the base body

11

,

31

may be composed of a composite material made of ceramics, i.e. a dielectric material, and resin, or a magnetic material such as ferrite.

In a case where the base body

11

,

31

is composed of a dielectric material, a high frequency signal propagates through the radiating electrode

14

,

34

at a lower speed, resulting in the wavelength becoming shorter. When the relative dielectric constant of the base body

11

,

31

is expressed as εr, the effective length of the conductor pattern of the radiating electrode

14

,

34

is given as εr

1/2

times and thus the effective length is increased. Hence, where the pattern length is kept the same, the current distribution region is increased in area. This allows the radiating electrode

14

,

34

to emit a larger quantity of radio waves, resulting in an advantage in enhancing the gain of the antenna.

Meanwhile, in the case of attaining the same antenna characteristics as conventional ones, the pattern length of the radiating electrode

14

,

34

can be set at 1/εr

1/2

, thus achieving miniaturization of the surface-mount type antenna

10

,

30

.

Note that fabricating the base body

11

,

31

using a dielectric material creates the following tendencies. If the value εr is less than 3, it approaches the relative dielectric constant as observed in the air (εr=1). This makes it difficult to meet the demand of the market for antenna miniaturization. By contrast, if the value εr exceeds 30, although miniaturization can be achieved, since the gain and the bandwidth of the antenna are proportional to the size of the antenna, the gain and the bandwidth of the antenna are sharply decreased. As a result, the antenna fails to provide satisfactory antenna characteristics. Hence, in the case of fabricating the base body

11

,

31

using a dielectric material, it is preferable to use a dielectric material having a relative dielectric constant εr which is kept within a range from 3 to 30. The examples of such a dielectric material include ceramic materials typified by alumina ceramics, zirconia ceramics, etc; and resin materials typified by tetrafluoroethylene, glass epoxy, etc.

On the other hand, in the case of fabricating the base body

11

,

31

using a magnetic material, the radiating electrode

14

,

34

has a higher impedance. This results in a low Q factor in the antenna, and the bandwidth is accordingly increased.

Fabricating the base body

11

,

31

using a magnetic material creates the following tendency. If the relative magnetic permeability μr exceeds 8, although a wider bandwidth can be achieved in the antenna, since the gain and the bandwidth of the antenna are proportional to the size of the antenna, the gain and the bandwidth of the antenna are sharply decreased. As a result, the antenna fails to provide satisfactory antenna characteristics. Hence, in the case of fabricating the base body

11

,

31

using a magnetic material, it is preferable to use a magnetic material having a relative magnetic permeability μr which is kept within a range from 1 to 8. The examples of such a magnetic material include YIG (Yttria Iron Garnet), Ni—Zr compound, and Ni—Co—Fe compound.

The radiating electrode

14

,

34

, the wide-area portion

15

,

35

, the feeding terminal

12

,

32

, and the ground terminal

13

,

33

are each made of for example a metal material which is predominantly composed of one selected from the group consisting of aluminum, copper, nickel, silver, palladium, platinum, and gold. In order to form various patterns using the aforementioned metal materials, conductor layers having desired pattern configurations are formed on the side surface and principal surface of the base body

11

,

31

by means of a conventionally-known printing method, a thin-film forming technique based on a vapor-deposition method, a sputtering method, etc., a metal foil bonding method, a plating method, or the like.

As the substrate

17

,

37

constituting the mounting substrate

16

,

36

, an ordinary circuit substrate made of for example glass epoxy or alumina ceramics is employed.

Moreover, the feeding electrode

18

,

38

and the ground electrode

19

,

39

are each composed of a conductor which is employed in an ordinary circuit substrate, such as copper or silver.

The ground conductor layer

20

,

40

, which is arranged on one side of the surface of the mounting substrate

16

,

36

with respect to the ground electrode

19

,

39

, is preferably composed of a conductor which is employed in an ordinary circuit substrate, such as copper or silver, and also the surface-mount type antenna

10

,

30

is preferably so mounted as to protrude from an edge of the ground conductor layer

20

,

40

. This is desirable in terms of enhancement of the bandwidth and gain of the antenna.

Note that mounting of the surface-mount type antenna

10

,

30

on the surface of the mounting substrate

16

,

36

, as well as connecting the feeding terminal

12

,

32

and the ground terminal

13

,

33

to the feeding electrode

18

,

38

and the ground electrode

19

,

39

, respectively, is preferably achieved by soldering, for example, through a reflow furnace.

EXAMPLE

Next, a description will be given as to an example of the surface-mount type antenna and the antenna apparatus of the first embodiment according to the invention. The example is built as a 1.575 GHz-band antenna designed for GPS. In the case of using an ordinary quarter-wavelength monopole antenna, the size of the antenna element is adjusted to be approximately 47 mm in length.

In the construction of the surface-mount type antenna

10

of the first embodiment of the invention shown in

FIG. 1

, there is prepared a base body

11

made of alumina ceramics (dimension: 10 mm×4 mm×3 mm). Then, using a silver conductor, a 1 mm-wide conductor pattern of helical conformation is formed. The conductor pattern, like the radiating electrode

14

shown in

FIG. 1

, has its one end formed into a wide-area portion

15

.

As the mounting substrate

16

, a 0.8 mm-thick glass epoxy substrate is used. The ground conductor layer

20

has the size of 40 mm×80 mm.

The surface-mount type antenna

10

is mounted on the mounting substrate

16

, thus achieving the antenna apparatus

21

of the invention. The antenna apparatus

21

is characterized by the center frequency of 1.575 GHz and the bandwidth of 30 MHz.

In a similar manner, the antenna apparatus

41

of the second embodiment of the invention as shown in

FIG. 4

is fabricated. The antenna apparatus

41

is also characterized by the center frequency of 1.575 GHz and the bandwidth of 30 MHz.

It is to be understood that the application of the invention is not limited to the specific embodiments described heretofore, and that many modifications and variations of the invention are possible within the spirit and scope of the invention.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are there fore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and the range of equivalency of the claims are therefore intended to be embraced therein.

Number	Name	Date	Kind
5748149	Kawahata	May 1998	A
6040806	Kushihi et al.	Mar 2000	A
6172646	Kawahata et al.	Jan 2001	B1

Surface-mount type antenna and antenna apparatus

Information

Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

Agents

CPC

US Classifications

Field of Search

US

International Classifications

Abstract

Description

Claims

Priority Claims (1)

US Referenced Citations (3)

Foreign Referenced Citations (1)